Compounded lubricating oil



United States Patent '0 Max W. Hill, Somerville, N. I, assignor to Esso Research and Engineering Company, a corporation of Delaware No Drawing. Application November 15, 1951,

Serial No. 256,595

Claims. (Cl. 252-45) The present invention is related to a new type of additive for motor lubricants. More particularly, it relates to compounded lubricants used in engines employing leaded fuels.

Internal combustion engines employing leaded fuels, such as those containing tetraethyl lead, operate under conditions such that various compounds of lead work their way past piston rings and tend to accumulate on various engine parts such as the oil ring slots, oil lines, and the like. These lead-containing accumulations frequently obstruct the normal flow of lubricating oils used in the engine. Such obstructions are particularly harmful in aviation engines where lead deposits are high and centrifugal action concentrates the lead deposits on vital engine parts.

It has been found, unexpectedly, that long chain, primary aliphatic mercaptans act as lead dispersants in lubricants. These mercaptans apparently react with or otherwise disperse the lead compounds resulting from the combustion of leaded fuels and holds such compounds in suspension. In addition to this unique property, the primary mercaptans also demonstrate potent bearing corrosion inhibiting properties.

It has been further found that the primary mercaptans are specific for this purpose, the secondary and tertiary aliphatic mercaptans being inetfective in preventing the deleterious effects arising from lead deposition. They often even aggravate such effects.

A relatively small amount of the primary mercaptans will act as lead dispersing agents. As a general rule, the lubricant should include in the range of about 1 to Wt. percent of primary mercaptan, based on the total lubricant, preferably about 3 to 10 wt. percent. The mercaptan used is a mono-thiol compound having the formula RCHzSH in which R is an hydrocarbon alkyl or alkenyl radical. The mercaptan should be of such molecular weight that it will be readily oil-soluble in the concentrations used. The mercaptans will have a relatively large number of carbon atoms in the alkyl chain, usually in the range of about 10 up to about carbon atoms, preferably from about 12 to 25, being required. The hydrocarbon radical may be straight chain or branched. Saturated aliphatic mercaptans are preferred. A particularly preferred primary mercaptan is n-octadecyl mercaptan.

Specific primary aliphatic mercaptans useful in the practice of the present invention include n-decyl mercaptan, n-dodecyl mercaptan, n-pentadecyl mercaptan, n-octadecyl mercaptan, n-docosyl mercaptan, 7,9,9-trimethyl dodecyl mercaptan, primary tetradecenyl mercaptans, 6,6,8,8-tetramethyl hexadecyl mercaptan and the like and their admixtures. The mercaptan should be substantially free of the secondary and tertiary isomers. The primary mercaptans may be prepared by procedures well known to the art.

The lubricating oil base stocks employed in the blended motor lubricating oils of this invention may be straight mineral lubricating oils, or distillates derived from par- 2 affinic, naphthenic, asphaltic .or mixed base crudes, or, if desired, various blended oils maybeemployed as well as residuals, particularly those from whichasphaltic constituents have been carefully removed. The mercaptans may also be added to synthetic lubricants comprising or composed of various synthetic polyestenand polyether and other types of synthetic materials useful as lubricating oils. The lubricating oils may vary considerably in viscosity and other properties, depending upon the particular use for which they are desired, but they usually range from about 40 to seconds Saybolt viscosity at 210 F.

In addition to the materials to be added according to the present invention, other additives may also be used such as pour depressors, heat thickened fatty oils, sulfurized fatty oils, organo-metallic compounds, metallic or other soaps, sludge dispersers, antioxidants, thickeners, viscosity index improvers, and oiliness agents.

The invention will be further illustrated by the following example in which is given the results of tests on the usefulness of compounds as lead dispersers and corrosion inhibitors. The example is given by way of illustration only, and is not to be construed as limiting the scope of the invention in any way.

Example I Blends containing 5 wt. percent of n-octadecyl mercaptan and 5 wt. percent of tertiary hexadecyl mercaptan, respectively, in a solvent extracted Coastal naphthenic oil of 60 seconds viscosity (Saybolt) at 210 F. were prepared for testing in a Lauson engine. A sample of the unblended base oil was also tested for comparison purposes. The test was conducted for a period of 25 hours, the Lauson engine being operated at 1800 R. P. M. with a 1.5 indicated kilowatt load, 300 F. oil temperature, and 295 F. Water jacket temperature. The fuel used had a Research octane number of 86 and contained 2.65 cc. tetraethyl lead per gallon of fuel. The oils were then rated on a demerit system wherein a perfectly clean surface is given a rating of 0, while a rating of 10 is given the worst condition that can be expected of that surface. Determinations were also made on the loss in weight of the copper-lead bearings used during the test. The results are shown in the following table:

In the reference run employing no additive, the oil ring slots of the engine were completely filled with lead deposits. In the case of the oil containing the n-octadecyl mercaptan, the oil ring slots were completely clean. The tertiary mercaptan, on the other hand, proved to be detrimental to engine cleanliness, and the oil containing it gave a much poorer performance than the unblended oil; furthermore, lead deposits were at least as bad when using the tertiary mercaptan-containing oil as in the case of the unblended oil.

What is claimed is:

1. A motor oil composition for use in the lubrication of internal combustion engines employing leaded fuels, which contains a lead dispersing amount of a primary aliphatic mercaptan having in the range of 10 to 30 carbon atoms, said lead-dispersing amount being in the range of about 1 to 15% by weight based on the total oil composition.

2. A composition as in claim 1 wherein said oil is a mineral-base lubricating oil.

is saturated and has in the range of 12 to 25 carbon atoms.

4. A composition asin claim 3 in which said mercaptan comprises n-octadecyl mercaptan.

5. A mineral base motor oil composition for lubricating internal combustion engines employing leaded fuels containing in the range of 3 to 10 wt. percent of a primary saturated aliphatic mercaptan having in the range of 12 to 25 carbon atoms in the chain, said mercaptan acting as a dispersing agent for lead compounds resulting from combustion of said leaded fuel.

References Cited in the file of this patent UNITED STATES PATENTS Sloane July 10, 1934 Garber et al. Jan. 1, 1952 OTHER REFERENCES Motor Oils and Engine Lubrication, C. W. Georgi, published 1950 by Reinhold Publishing Corp., New York,

10 Chapter X, pages 298 to 317. 

1. A MOTOR OIL COMPOSITION FOR USE IN THE LUBRICATION OF INTERNAL COMBUSTION ENGINES EMPLOYING LEADED FUELS, WHICH CONTAINS A LEAD DISPERSING AMOUNT OF A PRIMARY ALIPHATIC MERCAPTAN HAVING IN THE RANGE OF 10 TO 30 CARBON ATOMS, SAID LEAD-DISPERSING AMOUNT BEING IN THE RANGE OF ABOUT 1 TO 15% BY WEIGHT BASED ON THE TOTAL OIL COMPOSITION. 